How much water does a 22mm copper pipe hold per metre?

A 22mm copper pipe has an internal diameter of approximately 20mm, giving a volume of roughly 0.314 litres per metre (314 ml/m).

How do I calculate gas installation volume?

Sum the internal volume of every pipe section in the installation (π × r² × L for each section). Add the volume of any meters, regulators, and appliance connections. The total is the installation volume used for gas purge and tightness testing calculations.

How many litres are in a 15mm copper pipe per metre?

A standard 15mm copper pipe has an internal diameter of about 13mm, giving approximately 0.133 litres per metre.

What is the difference between pipe volume and pipe flow rate?

Pipe volume is the static amount of fluid the pipe can hold (litres or gallons). Flow rate is how much fluid passes a given point per unit of time (litres per minute or gallons per hour). Volume is a capacity; flow rate is a speed.

How do I convert pipe volume to gallons?

Calculate volume in litres first. Then divide by 4.546 for UK (imperial) gallons, or divide by 3.785 for US gallons. For example, 10 litres ÷ 4.546 = 2.2 UK gallons.

Pipe Volume Calculator – Litres, Gallons & m³ | Free Tool

Pipe Volume Calculator

Calculate the volume of any pipe in litres, gallons, or cubic metres. Works for water pipes, heating systems, gas installations, and industrial pipelines.

Knowing the volume of a pipe is one of the most practical calculations in plumbing, heating, and gas engineering. Whether you need to know how many litres of water are in a central heating system, how much fluid a pipeline holds before commissioning, or the installation volume of a gas pipework system for purge calculations, the same core formula applies.

This page gives you a free, instant pipe volume calculator plus the full formula, unit conversions, copper pipe volume charts, a dedicated gas installation volume guide, and worked examples covering domestic plumbing to large-bore pipelines.

Pipe Volume Calculator

Enter the pipe's internal diameter and length. Select your preferred units and click Calculate. Results are shown in litres, UK gallons, and cubic metres simultaneously.

Unit system

Internal diameter Enter the internal (bore) diameter in mm

Pipe length Enter the pipe length in metres

Please enter valid positive values for both diameter and length.

ℹ️

Use the internal diameter (also called bore or ID), not the outside diameter. For copper and PVC pipes, the internal diameter is smaller than the nominal size due to wall thickness. See the pipe size chart below for common internal diameters.

Pipe Volume Formula

A pipe is simply a hollow cylinder. The pipe volume formula is the standard cylinder volume formula applied to the internal bore:

V = π × r² × L

Where:

V= Volume of the pipe (in the same unit as your dimensions cubed) π= 3.14159… (pi) r= Internal radius = internal diameter ÷ 2 L= Length of the pipe

You can also write this using the diameter directly:

V = π × (D/2)² × L = (π/4) × D² × L

D= Internal diameter of the pipe

Unit conversions after calculating

The formula gives you cubic units. To convert to useful real-world units:

Input units	Result in	To get litres	To get UK gallons	To get m³
millimetres (mm)	mm³	÷ 1,000,000	÷ 4,546,090	÷ 1,000,000,000
centimetres (cm)	cm³	÷ 1,000	÷ 4,546.09	÷ 1,000,000
metres (m)	m³	× 1,000	× 219.969	× 1
inches (in)	in³	× 0.016387	× 0.003605	× 0.000016387
feet (ft)	ft³	× 28.3168	× 6.2288	× 0.028317

Quick reference: gallons conversion

1 UK (imperial) gallon = 4.546 litres
1 US gallon = 3.785 litres
1 litre = 0.2200 UK gallons
1 litre = 0.2642 US gallons
1 m³ = 219.97 UK gallons = 264.17 US gallons

⚠️

UK and US gallons are not the same. A UK imperial gallon is about 20% larger than a US gallon. Always confirm which gallon is being used, especially on imported equipment or American plumbing guides.

Pipe Volume Charts and Tables

The tables below give you pre-calculated volumes for the most common pipe sizes used in the UK and internationally. All values use the typical internal diameter for each nominal size.

Copper pipe volume chart – litres per metre and gallons per foot

Standard UK copper pipe (to EN 1057). Internal diameters are approximate; actual IDs vary slightly by manufacturer and grade.

Nominal OD (mm)	Typical ID (mm)	Wall (mm)	L per metre	mL per metre	UK gal / metre	US gal / foot	m³ per 10m
6 mm	4.0 mm	1.0	0.013	12.6	0.0028	0.00034	0.000126
8 mm	6.0 mm	1.0	0.028	28.3	0.0062	0.00075	0.000283
10 mm	8.0 mm	1.0	0.050	50.3	0.0111	0.00133	0.000503
15 mm	13.0 mm	1.0	0.133	132.7	0.0292	0.00351	0.001327
22 mm	20.0 mm	1.0	0.314	314.2	0.0691	0.00831	0.003142
28 mm	26.0 mm	1.0	0.531	530.9	0.1168	0.01405	0.005309
35 mm	32.6 mm	1.2	0.835	835.2	0.1836	0.02210	0.008352
42 mm	39.6 mm	1.2	1.231	1231	0.2708	0.03258	0.01231
54 mm	51.6 mm	1.2	2.093	2093	0.4603	0.05540	0.02093
67 mm	64.0 mm	1.5	3.217	3217	0.7078	0.08516	0.03217
76 mm	73.0 mm	1.5	4.185	4185	0.9206	0.11077	0.04185

Larger bore pipe volume chart – 100mm to 500mm

For commercial and industrial applications. Internal diameter is taken as OD minus a typical wall thickness; verify your specific pipe schedule or standard.

Nominal size	Approx ID (mm)	L per metre	UK gal / metre	m³ per 100m	m³ per 1 km
100 mm (4 in)	98 mm	7.54	1.659	0.754	7.54
150 mm (6 in)	147 mm	16.97	3.733	1.697	16.97
200 mm (8 in)	196 mm	30.17	6.637	3.017	30.17
250 mm (10 in)	246 mm	47.52	10.453	4.752	47.52
300 mm (12 in)	296 mm	68.83	15.143	6.883	68.83
400 mm (16 in)	394 mm	121.9	26.81	12.19	121.9
500 mm (20 in)	493 mm	191.0	42.02	19.10	191.0

PVC and MDPE pipe volume – common sizes

Nominal OD (mm)	Typical ID (mm)	Material	L per metre	UK gal / metre
20 mm	16.2 mm	MDPE (water)	0.206	0.0453
25 mm	20.4 mm	MDPE (water)	0.327	0.0719
32 mm	26.2 mm	MDPE	0.539	0.1186
20 mm	15.3 mm	PVC Class C	0.184	0.0405
32 mm	27.0 mm	PVC Class C	0.573	0.1260
40 mm	34.4 mm	PVC Class C	0.929	0.2044
50 mm	43.4 mm	PVC Class C	1.480	0.3256
110 mm	103.6 mm	PVC soil/drain	8.430	1.855

Steel pipe volume – schedule 40

Nominal pipe size	OD (mm)	ID Sch 40 (mm)	L per metre	UK gal/ft	US gal/ft
½ in	21.3	15.8	0.196	0.0132	0.0158
¾ in	26.7	20.9	0.343	0.0231	0.0278
1 in	33.4	26.6	0.556	0.0374	0.0450
1½ in	48.3	40.9	1.314	0.0884	0.1064
2 in	60.3	52.5	2.165	0.1457	0.1753
3 in	88.9	77.9	4.767	0.3208	0.3862
4 in	114.3	102.3	8.213	0.5527	0.6651
6 in	168.3	154.1	18.66	1.2566	1.5118

Volume of Water in Pipe Systems

Calculating the volume of water in a pipe is essential for several practical tasks:

Central heating systems

When you're sizing a heating system, you need to know the total water volume to correctly size the expansion vessel, determine the correct inhibitor dosage, and calculate chemical flush volumes. A typical UK domestic system holds 8–15 litres in the pipework alone, plus the boiler heat exchanger and radiators.

System flushing and water treatment

Powerflush contractors and plumbers need to know the total water volume to dose inhibitor, cleaner, or biocide at the correct concentration. Under-dosing leaves systems vulnerable to corrosion and scale; over-dosing wastes money and can affect system components.

Filling time and pressure calculations

Knowing how much water a pipe or pipeline holds lets you estimate filling time at a given flow rate. It also informs hydraulic calculations: a full pipe under pressure exerts more force than engineers might assume if they overlook the water mass.

Stored water in pipe networks

In commercial and industrial settings, dead-legs (pipe sections that see infrequent flow) can accumulate stagnant water. Legionella risk assessments require accurate pipe volume data for every section of a building's hot and cold water system.

✅

For a full central heating system, add the volume from pipework calculations to the volume from your heating system water volume calculator, which also accounts for radiator water content.

Gas Installation Volume Calculator

Gas engineers need to calculate the installation volume of pipework for two key purposes: gas tightness testing and gas purging calculations. Both are Gas Safe requirements under IGEM/UP/1B and the Gas Safety (Installation and Use) Regulations 1998.

What is gas installation volume?

Gas installation volume is the total internal volume of all the pipework and components in a gas installation, measured in cubic metres (m³) or litres. It includes every pipe section from the outlet of the emergency control valve (ECV) to the appliance connections, plus the volume of meters, governors, flexible connections, and any other components within the installation.

How to calculate gas installation volume

Sum the volume of each pipe section using the standard cylinder formula:

Installation Volume = Σ (π × r² × L) for each pipe section

Then add the volume of the gas meter (typically stamped on the meter or available from the meter data sheet) and any other in-line components.

Worked example: domestic gas installation

Scenario: 3-bedroom semi-detached house

10m of 22mm copper pipe (ID = 20mm): π × 0.010² × 10 = 0.00314 m³ = 3.14 L
5m of 15mm copper pipe (ID = 13mm): π × 0.0065² × 5 = 0.000664 m³ = 0.66 L
3m of 10mm copper pipe (ID = 8mm): π × 0.004² × 3 = 0.000151 m³ = 0.15 L
Gas meter volume (U6): approximately 0.0016 m³ = 1.6 L
Total installation volume ≈ 0.00575 m³ ≈ 5.55 litres

Gas purging

When introducing gas to a new or recommissioned installation, the pipework must be purged of air. The purge volume required depends on the total installation volume. For installations below 0.035 m³ (35 litres), the standard purge procedure under IGEM/UP/1B applies. Larger installations require a different approach.

⚠️

Gas Safe requirement: All gas work must be carried out by a Gas Safe registered engineer. Installation volume calculations affect the tightness testing pressure decay limits. Always verify calculations against current IGEM/UP/1B guidance and your employer's procedures.

Pressure decay limits and installation volume

Under the let-by test and tightness test procedures, the acceptable pressure drop depends on the installation volume. A larger volume means a smaller pressure drop is acceptable for a given leak rate. Gas engineers must know the installation volume to determine the correct pass/fail criterion for the test gauge reading after the stabilisation period.

Common gas pipe materials and internal diameters

Material	Nominal size	OD (mm)	Typical ID (mm)	L per metre
Copper (EN 1057)	10 mm	10	8.0	0.0503
Copper (EN 1057)	15 mm	15	13.0	0.1327
Copper (EN 1057)	22 mm	22	20.0	0.3142
Copper (EN 1057)	28 mm	28	26.0	0.5309
Steel (BS 1387)	½ in BSP	21.3	15.8	0.1961
Steel (BS 1387)	¾ in BSP	26.7	20.9	0.3431
Corrugated SS (CSST)	DN15	—	~13.5	~0.143
PE/yellow MDPE	32 mm	32	26.2	0.539

Pipe Capacity vs Pipe Volume

These two terms are often used interchangeably, but they describe slightly different things:

Pipe volume (or pipe capacity) is the static amount of fluid the pipe can hold at any one time. It's a fixed value for a given pipe diameter and length.
Flow rate is how much fluid passes through the pipe per unit of time (litres per minute, m³/hour, etc.). Flow rate depends on pressure, pipe diameter, fluid viscosity, and pipe roughness.
Pipe capacity in hydraulic engineering sometimes refers to the maximum flow rate the pipe can carry at a given velocity limit — this is different from the volume it holds.

For filling calculations (how long to fill a pipeline), you use the static volume. For sizing calculations (will this pipe deliver enough flow?), you need the hydraulic capacity and flow rate. See our pipe flow rate calculator for flow and velocity calculations.

Hydraulic pipe capacity

The hydraulic capacity of a pipe is influenced by its internal diameter (the most important factor), wall roughness, fluid velocity, and pressure. Doubling the diameter increases the flow capacity by a factor of four, because the cross-sectional area — and therefore the volume it can carry — increases with the square of the diameter.

Pipe Material Volume Differences

The volume a pipe holds depends entirely on its internal diameter, not the nominal size marked on the outside. Different materials and pipe standards result in different wall thicknesses, which means the internal diameter varies even between pipes of the same nominal size.

Copper pipe

UK copper pipe is made to EN 1057. The most common type (Table X, or R250) has a wall thickness of about 0.7–1.5mm depending on diameter. A nominal 15mm copper pipe has an outside diameter of exactly 15mm and an internal diameter of approximately 13mm. Always check the manufacturer's datasheet for the exact internal diameter if precision matters.

PVC pipe

PVC pipe comes in several pressure classes (Class C, Class D, Class E for cold water service) and each class has a different wall thickness for the same outside diameter. Class C (lower pressure) has a thinner wall and therefore a larger internal volume than Class E (higher pressure). The nominal OD is fixed; the ID varies by class.

Steel pipe

Steel pipe uses a "schedule" system where the schedule number determines wall thickness. Schedule 40 is the most common. A 2-inch Schedule 40 steel pipe has an ID of 52.5mm; the same pipe in Schedule 80 has an ID of 49.3mm — a meaningful difference for accurate volume calculations.

MDPE (medium-density polyethylene)

MDPE pipe, commonly used for underground water mains and gas supplies in the UK, is sized by outside diameter. The SDR (standard dimension ratio) determines the wall thickness. Blue MDPE (water) and yellow MDPE (gas) often share the same outside diameter but may have different wall specifications. Always use manufacturer data for internal diameter.

⚠️

For any safety-critical calculation (gas purging, pressure testing, water treatment dosing), use the actual internal diameter from the manufacturer's technical specification, not a nominal or assumed value.

Step-by-Step Pipe Volume Examples

Example 1: Domestic copper pipe (15mm)

Scenario: How many litres are in 12 metres of 15mm copper pipe?

Internal diameter of 15mm copper pipe = 13 mm = 0.013 m
Internal radius = 0.013 ÷ 2 = 0.0065 m
Apply the formula: V = π × (0.0065)² × 12 = π × 0.00004225 × 12
V = 3.14159 × 0.000507 = 0.001593 m³
Convert to litres: 0.001593 × 1000 = 1.59 litres
Convert to UK gallons: 1.59 ÷ 4.546 = 0.35 UK gallons

Example 2: Central heating system pipework

Scenario: Total water volume in a 2-storey house heating system pipework

20m of 22mm pipe (ID 20mm): π × 0.01² × 20 = 0.00628 m³ = 6.28 L
15m of 15mm pipe (ID 13mm): π × 0.0065² × 15 = 0.00199 m³ = 1.99 L
8m of 10mm pipe (ID 8mm): π × 0.004² × 8 = 0.000402 m³ = 0.40 L
Total pipework volume: 6.28 + 1.99 + 0.40 = 8.67 litres
Add radiator water content (approx 1.5L per standard double panel radiator × 8 rads = 12L)
Add boiler heat exchanger (typically 1.5–3L, check manufacturer data)
Estimated total system volume ≈ 22–24 litres

Example 3: Pipeline fill calculation (large bore)

Scenario: How long to fill a 200m run of 100mm pipe at 30 L/min?

Internal diameter ≈ 98mm = 0.098m
V = π × (0.049)² × 200 = π × 0.002401 × 200 = 1.508 m³ = 1,508 litres
Fill time = Volume ÷ Flow rate = 1,508 ÷ 30 = 50.3 minutes

Example 4: Gas installation volume calculation

Scenario: Calculate total installation volume for a commercial kitchen gas supply

25m of 28mm copper (ID 26mm): π × 0.013² × 25 = 0.01327 m³ = 13.27 L
10m of 22mm copper (ID 20mm): π × 0.01² × 10 = 0.00314 m³ = 3.14 L
6m of 15mm copper (ID 13mm): π × 0.0065² × 6 = 0.000796 m³ = 0.80 L
Gas meter (U16): volume ≈ 0.0040 m³ = 4.0 L (from meter data sheet)
Flexible connections, governor, manifold: approximately 0.5 L
Total installation volume ≈ 0.02167 m³ ≈ 21.71 litres
This is below 0.035 m³ so standard IGEM/UP/1B tightness test procedure applies

Example 5: Volume in imperial units (gallons per foot)

Scenario: Volume of ¾-inch copper pipe in US gallons per foot

¾ inch copper pipe: ID = approximately 0.785 inches (standard Type L)
Radius = 0.785 ÷ 2 = 0.3925 inches
Volume per foot = π × (0.3925)² × 12 = π × 0.1541 × 12 = 5.809 in³/ft
Convert to US gallons: 5.809 × 0.004329 = 0.0251 US gal/ft
Convert to UK gallons: 5.809 × 0.003605 = 0.0209 UK gal/ft
Convert to litres: 5.809 × 0.016387 = 0.0952 L/ft

Common Pipe Volume Calculation Mistakes

⚠️ Using outside diameter instead of ID

This is the most common error. Always use the internal (bore) diameter. For a 22mm copper pipe, the OD is 22mm but the ID is ~20mm — a 10% error if you use the wrong value.

⚠️ Forgetting wall thickness on large pipes

For small pipes the difference is modest, but on 200mm or larger pipes, a 5mm wall thickness reduces the bore area significantly. Always check the pipe schedule or data sheet.

⚠️ Mixing metric and imperial units

Putting an inch-based diameter into a formula expecting millimetres will produce a wildly wrong result. Check your units before calculating.

⚠️ UK gallons vs US gallons confusion

A UK imperial gallon is 4.546 litres; a US gallon is 3.785 litres. American plumbing data sheets use US gallons. Using the wrong conversion creates an 18% error.

⚠️ Not measuring actual pipe length

Pipe runs include bends, offsets, and allowances for fittings. A straight-line estimate of a pipe run is always shorter than the actual pipe length. Measure along the pipe centreline.

⚠️ Ignoring fitting and component volumes

For gas installation volume calculations, the meter, governor, and flexible connections add volume that must be included. For heating systems, radiators and the boiler heat exchanger hold significant water.

Frequently Asked Questions

How do you calculate the volume of a pipe?

Use the formula V = π × r² × L, where r is the internal radius (half the internal diameter) and L is the pipe length. Make sure all measurements use the same unit. Divide the result by 1,000 if your dimensions are in centimetres to get litres, or divide by 1,000,000 if working in millimetres.

What is the formula for pipe volume?

The pipe volume formula is V = π × (D/2)² × L or equivalently V = (π/4) × D² × L, where D is the internal diameter and L is the length. This is the standard cylinder volume formula applied to the hollow bore of the pipe. The result is in cubic units; divide appropriately to get litres, gallons, or m³.

How do you calculate pipe volume in litres?

Measure the internal diameter in metres and the length in metres. Calculate V = π × (D/2)² × L in m³. Then multiply by 1,000 to get litres. Alternatively, measure diameter in mm, calculate V in mm³, and divide by 1,000,000 to get litres. The calculator at the top of this page does this automatically.

How do you calculate pipe volume in m³?

Measure the internal diameter and length in metres. Apply V = π × (D/2)² × L. The result is directly in cubic metres (m³). For example, a 100mm (0.1m) ID pipe that is 50m long has a volume of π × 0.05² × 50 = 0.3927 m³.

How much water does a pipe hold per metre?

This depends on the internal diameter. Common values for copper pipe are: 15mm pipe ≈ 0.133 L/m; 22mm pipe ≈ 0.314 L/m; 28mm pipe ≈ 0.531 L/m; 54mm pipe ≈ 2.093 L/m. See the full chart above for all sizes including gallons per foot and m³ values.

How many litres are in a 22mm pipe per metre?

A standard 22mm copper pipe (EN 1057) has an internal diameter of approximately 20mm. Volume per metre = π × 0.01² × 1 = 0.000314 m³ = 0.314 litres per metre (314 ml/m). Over 10 metres this gives 3.14 litres.

How do you calculate gas installation volume?

Calculate the internal volume of every pipe section using V = π × r² × L for each section. Add the meter volume (from the meter data sheet), governor, flexible connections, and any other components within the installation boundary. The total is your gas installation volume in m³ or litres, used for tightness testing pressure decay limits under IGEM/UP/1B.

What is the difference between pipe volume and pipe capacity?

Pipe volume (or pipe capacity in the static sense) is the amount of fluid the pipe can hold at any given moment — a fixed value for a given size and length. Hydraulic pipe capacity refers to the maximum flow rate the pipe can carry, which depends on pressure, velocity limits, and fluid properties. Volume is used for filling and dosing calculations; flow capacity is used for system sizing.

How do I convert pipe volume from litres to UK gallons?

Divide litres by 4.546 to get UK imperial gallons. For example, 10 litres ÷ 4.546 = 2.20 UK gallons. To go the other way, multiply UK gallons by 4.546. Note: US gallons use a different conversion (1 US gal = 3.785 litres).

What is pipe capacity?

Pipe capacity is the maximum volume of fluid a pipe can contain, determined by its internal diameter and length. It is distinct from flow rate or hydraulic throughput capacity. To calculate it, use the standard pipe volume formula: V = π × r² × L.

How many gallons per foot in a ¾ inch pipe?

For a ¾ inch copper Type L pipe (ID ≈ 0.785 in): approximately 0.025 US gallons per foot, or 0.021 UK gallons per foot. For ¾ inch Schedule 40 steel pipe (ID ≈ 0.824 in): approximately 0.028 US gallons per foot.

Related Calculators

Use these tools alongside the pipe volume calculator for complete plumbing, heating, and gas system design:

Pipe Sizing Calculator Pipe Flow Rate Calculator Pressure Drop Calculator Gas Pipe Sizing Calculator Pipe Velocity Calculator Heating System Volume Calculator Pump Head Calculator Water Pipe Sizing Calculator

This page covers pipe volume calculations for water systems, central heating, gas installations, and industrial pipelines. All formulas follow standard engineering practice. For safety-critical applications including gas installation volume, always verify calculations with a qualified Gas Safe registered engineer.

Metric & Imperial Litres · Gallons · m³ Copper · Steel · PVC · MDPE Gas Installation IGEM/UP/1B EN 1057

Last updated: May 2026

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